A comparison of copper(I) and copper(II) bound to thioether ligands : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University

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Abstract

The structures of Cu(II) (DTH)2(BF4)2 (where DTH = 2,5-dithiahexane) and Cu(I) (DTO)2BF4
(where DTO = 3,6-dithiaoctane) have been investigated by single crystal X-ray diffraction techniques. After full matrix least squares refinement of the structures, with anisotropic temperature factors for all non hydrogen atoms in the Cu(II) structure, and for all atoms larger than fluorine in the Cu(I) structure, the conventional R factor converged to a final value of 0.057 for the Cu(II) structure, and 0.082 for the Cu(I) complex. The dark red crystals of the Cu(II) complex belong to the centrosymmetric monoclinic space group P2 1/c. with a = 8.082(3)Å, b = 10.282(3)Å, c = 11.893(4)Å and β = 115.3 degrees. Two
dithiahexane ligands and two BF4-ions were found to co-ordinate to the Cu(II) ion to form a tetragonally
distorted octahedron, with four Cu(II)-S bonds averaging 2.317Å in length, and two longer Cu(II)-F bonds averaging 2.576Å. The four sulphur atoms are part of two five membered Cu(II)-S-C-C-S rings in which both carbons are on the same side of the plane containing the copper and sulphur atoms. The colourless crystals of the Cu(I) complex were obtained in the non-centric orthorhombic space group Pna2 1, with a
= 14.581(2)Å, b = 13.421(2)Å and c = 10.781(2)Å. The molecules exist as discrete monomeric species, with no co-ordination of the BF4- ion to the metal ion. The two ligand molecules co-ordinate to the Cu(I)
ion to form a distorted tetrahedron, with the S-Cu(I)-S angles varying between 94.0 and 121.1 degrees. The four Cu(I)-S bonds average 2.307Å in length, and hence are approximately equal to the Cu(II)-S bonds (within experimental error). The two five membered Cu(I)-S-C-C-S rings are both in a gauche conformation, with one carbon below the plane containing the Cu(I) and S atoms, and the other above. The BF4- ion was disordered and was refined using rigid group restrictions. Cu-S co-ordination is thought
to occur in some copper containing oxidation-reduction proteins. The observation of similar Cu-S bond distances when Cu(I) and Cu(II) are co-ordinated to thioether ligands (resembling the side chain of the amino acid methionine) may therefore be of direct relevance to the copper co-ordination in such proteins.